


Yukio x Rin

by Kitten1134



Category: Ao no Exorcist | Blue Exorcist
Genre: Alternate Universe, Boys In Love, Fluff and Smut, Implied Sexual Content, LGBTQ Character, Lemon, M/M, Out of Character, Romance
Language: English
Status: In-Progress
Published: 2020-09-13
Updated: 2020-09-13
Packaged: 2021-03-06 19:41:34
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 3,783
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26444335
Author URL: https://archiveofourown.org/users/Kitten1134/pseuds/Kitten1134
Summary: What if...Rin and Yukio aren't blood related brothersShiro is still aliveYuri didn't die during birthRin knew he was the son of Satan beforehandYukio's a little bit olderYukio and Rin are also dating.Shiro Fujiomoto took Rin in after being sent by the True Cross order to execute both Yuri and Satan's child. Baby Rin smiled at Shiro, changing something inside of him. Despite what he had originally thought he couldn't bring himself to kill someone he had grew to care about and a new born child. Even if the two of them involved Satan.Shiro hides Yuri and Rin from the Vatican inside his monastery.Shiro already has an adopted son, Yukio.Yukio and Rin grow up together in the monastery and become super close like brothers. But their feelings toward each other change as they grow older.Keep in mind:-I don't own blue exorcist, Kazue Kato does-I own none of the characters unless (except for my OC's)-Characters may act a little OOC,-This is yaoi. Maybe a bit more on the shounen ai side, depending on what I come up with.-Yukio= Dom/TopRin= Sub/bottomIf any of this bothers you, then I wouldn't recommend reading
Relationships: Okumura Rin/Okumura Yukio
Comments: 3
Kudos: 37





	1. Prologue

**Author's Note:**

> I know I mentioned this in the description, but just to remind you of a few things: 
> 
> -Rin and Yukio are NOT blood related in this AU, but they were raised in the same house.  
> -There may be some smut in the future, but there will primarily be implied smut.  
> -Rin is the submissive one

It was the most horrific thing to ever happen in True Cross's history.

Every exorcist had burst into flames. Their screams of agony and fear could be heard. Many lives had been lost that night. Yuri Egin, a beautiful young woman with flowing brown hair and blue eyes had been tied to the stake. She had been labeled a witch and was to being burned to death for siding with Satan and becoming impregnated with his spawn.   
Just as the flames licked her feet, she cried out to Satan for him to rescue her.   
Satan heard her cry all the way from Gehenna. 

As soon as he heard her call out to him he immediately made his way to save his human lover. Out of all his past love interests, she was the one he had truly cared for.

Within minutes he came out of the portal which had lead him straight to Assiah. He had reached Assiah only to find that it was impossible to reach Yuri, for he did not have a vessel to possess. It would be relatively easy to find a host for any other demon, but not for Satan. His flames were too powerful, which meant that every vessel he possessed was doomed to die. 

Very few bodies were immune to his powerful blue flames, he only had to find a human who was able to contain him. He jumped from vessel to vessel as quick as he could, each one bursting into flames and burning alive. He was running out of options, Yuri was screaming in agony as she was slowly being burnt to death, her legs were already on fire. 

If he didn't hurry, Yuri would vanish before his eyes, and so would everything they worked for. They had dreamed of a world where demons and humans could coexist. They would prove to the world both beings could get along, starting with their child; who would have the blood of a human and demon. He would be the proof that both humans and demons could get along.But if he were too late, then all of that would disappear. This was the first thing he was ever passionate about. 

Yuri was special to him, she was the only human, let alone exorcist, who would give demons the time of day. 

There was only one last vessel he could try, Ernst Egin. 

Yuri's father. 

It was his fault that this was happening in the first place. He couldn't find it in his heart to accept their relationship. He thought anyone who associated themselves with demons, especially Satan, where wicked witches possessed by evil spirits. And were to be locked up or executed. He had arranged for Yuri, his own daughter, to be executed.   
Satan possessed Ernst, only to find it was a perfect vessel for him. He made his way to Yuri as fast as his vessel could take him. 

"Yuri!"

"Satan! Satan is that you?" 

"Yes, hold on my dear." 

He untied Yuri from the stake and escaped with her, leaving his unconscious host. They had escaped into the forest. 

~*~*~*~

Later on, Yuri gave birth to her and Satan's child.   
He was a lovely baby boy with little blue hairs. Satan, left without a vessel, could only watch his child be born from a distance, but Yuri understood. 

Shiro Fujimoto, paladin and member of the true cross order, along with the demon king of time, Samael, who went by his alias Mephisto Pheles. Had been sent by the Vatican to execute the spawn of Satan and Yuri Egin, who had escaped from the execution.   
Deep down, it pained Shiro to kill the girl he had grown quite fond of. She was so young, so free spirited, he cared for her like the daughter he never had or wanted. But as paladin he had to follow the Grigori's orders. 

He had found her resting on blankets and pillows in a cave. 

"Rin." She said holding a little blue bundle which was engulfed in blue flames. "I'll name him Rin." 

  
Shiro held the sword, Mephisto gave him a look that said 'well, on with it.' He grasped the sword, ready to strike. Yuri smiled down at her baby with tears threatening to leave the corner of her eyes. Yuri had passed out shortly after, in critical condition. Her legs were badly burnt and her breaths were short and raspy. 

Shiro picked up the child to execute it. Now was his chance, there was no struggle. That was when baby Rin looked right at him and smiled an adorable, toothless smile and giggled.

In that moment, something in Shiro changed.   
He couldn't find it in him to kill this child, or Yuri. Mephisto noticed his quick change in actions. 

"I can't do it..." Shiro said softly. 

"Can't do what exactly?" Mephisto asked even though he already knew the answer. 

"We can't kill him, even if he is the spawn of Satan. He's only an infant." He had the smile of an angel, something so cute and pure couldn't have been evil. 

"Well then, what are we to do with them?" Mephisto asked. Being the demon king of time, he already knew. 

"I'm going to help take care of him." Mephisto took the kurikara from Shiro and said a chant, the baby's flames went into the sword. 

"What are you doing?" 

"I'm sealing his flames into this sword. If we're going to hide him from the Vatican we can't have him shooting flames from his body." 

Shiro nodded in agreement. He took the child in his arms while he ordered Mephisto to carry Yuri. They would be hiding the two of them in his monastery, to protect them from the demons and exorcist who would be coming for them without a doubt. 

"Rescuing another child all within the same month, how are you going to raise the two of them?" Mephisto asked, he had rescued another baby who's family had been killed by demons. The poor child lost his parents and received a temp taint from the demons who tried to kill him. Shiro exorcised the demons and rescued the baby, deciding to raise it as his own. The child's name was Yukio. He had teal eyes and small dark brown hairs. 

Satan watched the exorcist and his second eldest son, who had betrayed him and sided with the enemies, leave with his youngest child and unconscious lover. Without a vessel there was nothing he could do about it. He'd get the two of them back some day. 

~*~*~*~ 

~five years later~ 

A young boy ran around outside just beyond the monastery in a small town. He had unnatural coloured dark navy blue hair and sapphire eyes. He was around the age of five. 

"You'll never catch me Yukio! I'm too fast for you!" He giggled, he and another little boy were playing tag. The other little boy had teal eyes, dark brown hair and a few moles spread across his face. We wore big round glasses over his big round eyes. He was struggling to keep up with the other, he traveled at an unnatural speed for a regular kid their age. He huffed and puffed cutely as he ran as fast as his tiny legs could take him. 

He felt himself bump into something hard sending the small boy flying backwards. He fell on his butt making a small 'oof!' Sound. 

He looked up to see another kid. He was very tall, and older than the small boy with glasses. His name was Kosuke, he was in the third grade, he appeared very tall and scary looking to a five year old. He had blonde hair and brown eyes. 

"Well well well, if it isn't the FOUR EYED BABY!" Two others stood behind Kosuke, one of them he recognized at Reiji Shiratori, the same age as he was. He was tough for his age. So he was seen hanging out with the older, tougher kids, at school. Yukio trembled in fear and crawled backwards. 

"Awe, is the little baby scared?" He asked in a mocking cutesy tone of voice. He laughed and kicked him in the side. Yukio, being the sensitive and small boy he was, started crying. 

"Hey!" A small voice yelled. "Stay away from him!" In a flash, he was on them, punching and kicking them with all his might. The blunette was very strong despite his small stature. He took on all three boys and sent them running, crying for their mommies. 

He ran over to the other brunette and kneeled next to him. "Yuki! Are you ok?" He asked worried for his friend. Yukio nodded, still with tears in his eyes. 

"I'm fine Rin." Rin gave Yukio a hug, then helped him up pulling him toward the monastery. 

*~*~*~*

Although Yukio was the one kicked and pushed, Rin had received most of the injuries from fighting the other older boys. 

Shiro cleaned his off his cuts and bruises. Rin winced at the pain. 

The older man sighed. "Rin, what did I tell you about getting into fights?" 

"..." 

"Well?!" Shiro raised his voice.

"Not to." He said softly with a guilty look. "But it wasn't my fault this time! Promise! He started it!" Rin defended himself. 

"That doesn't matter. You know you're a lot stronger than them, and it's never ok to hit others." 

"But-"

"No buts!" Yukio peered at them from bathroom door, he watched his father clean Rin's cuts and scrapes. He felt kind of guilty, Rin got hurt protecting him...

Shiro left the bathroom. Rin sat on the closed toilet seat. Yukio hesitantly entered the washroom. 

"Rin...?" 

Rin looked over at the door to see his friend. 

"YUKI!" His face lit up like a Christmas tree. 

Yukio walked closer to Rin, Rin noticed something was wrong. 

"What's wrong Yuki?" He asked concerned. Yukio had a frown a furrowed eyebrows. 

"I'm sorry Rin!" 

"What do you mean? Sorry for what?" 

"You're hurt b'cause of me!" Yukio cried. Rin pulled Yukio into a hug. 

"No, I was saving you from them." 

"You didn't have to do that."

"Yes I did." 

"Why?" 

"Cause I love Yuki!" He giggled and squished their faces together whiles hugging him tighter. 

"I love you too Rin." He said hugging him back. 

*flash!* 

"Awe~ isn't that cute." Shiro chuckled. He had taken a picture of the two boys hugging. 

"It sure is." Yuri said standing next to Shiro. 

She had scars on her legs from being burnt that night, she could never walk the same after that, but she was making a slow recovery. Yuri was quite ill, she became sick after giving birth to Rin. Her illness didn't seem to be getting better though. 

They were all very close, Yukio and Rin were like brothers. Yuri was like Yukio's mother figure and Shiro was Rin's father figure. 

Yuri hardly left the monastery since she and Rin were still in hiding from the Vatican. For all they knew, they were dead. Satan had barely any contact with Yuri. Shiro was good at keeping him away from his family. 

Rin was aware of his demon heritage, he didn't yet know of his powers, since they were sealed off. Shiro was against Rin learning about his true family, but Yuri felt it was necessary for Rin to know his father. She and Satan worked hard for this, for Rin. It wasn't fair to him if his own son knew nothing about him. Despite what people thought, the demon God could be kind. 

Rin only met Satan once, Shiro felt that once was enough and created strong seals and barriers to keep demons out. Rin being half human could make it through the barriers. 

Satan never quit trying to get his family back, but Shiro was strong willed and had the strength to keep Satan away. 

Yukio and Rin were playing in the room that they shared together. Those two boys were inseparable. It would be that way forever if they could help it.


	2. Chapter 1

**Summary for the Chapter:**

> Satan attacks the monastery while trying to retrieve his son.

Eleven years have passed by. Not too many years ago Yuri Egin had passed away from her unknown illness. Rin was absolutely devastated. He lost his mother, his only blood related family. He was basically an orphan now. Shiro Fujimoto still took care of Rin, it was a little more challenging raising him with out Yuri there to calm the young boy. 

Demons did not stop coming for Rin, Satan would not rest until he had his son to complete his family. Yuri was now with him in Gehenna. Once she had died, her soul was sent to Gehenna, along with all of the other souls who were once possessed by the demon God. She ruled as the queen of Gehenna by his side. Now all he needed was his youngest son.

One day Shiro had come home to a seven year old Yukio who was crying. Yukio didn't understand why he saw the things that he saw, it was scary. Shiro asked him if he would like to join him and become an exorcist. He told him that he would be able to help him protect Rin. Yukio's eyes lit up.   
He would get to protect Rin?!

He would give anything to be able to save Rin for a change. He cared for him, he was like his brother. Rin was alway rescuing Yukio from his bullies, and getting hurt in the process. Yukio would become Rin's knight in shining armour and defend him from the bullies. 

He went into intense training to become an exorcist. By the age of 12 he had completed his training and became the world's youngest exorcist. He had been secretly training to become an exorcist. He had never kept secrets from Rin before, but Shiro said it was for the best that he did not know. He wanted to keep Rin away from anything that had to do with demons. Shiro didn't want to run the risk of demons coming for his boy. He knew fully well that all of these demons that Yukio saw around the monastery were after Rin. They had been sent by Satan to come retrieve their prince and bring him home. They kept Rin under constant surveillance. What they didn't know was that they didn't do as good a job of keeping an eye on Rin as they thought. Rin would be left alone a lot. He had no friends besides Yukio because everyone hated him. They called him names like 'beast' and 'demon'. On the inside Rin was like _'yeah, I know'._

Little hobgoblins, low level demons, and spirits who didn't reveal themselves to humans would keep him company. Him being half demon, he was able to see all of the demons. He just didn't make that big of a deal when he came across them, he just let them be. Shiro and Yukio felt they were doing such a great job keeping him from interacting with demons. When in reality, Rin just carried on with his business when he saw them. 

The demons would refer to him as their "king" or "young master".

A lot had happened during those past eleven years. 

*~*~*~*

The monastery was being attacked. Shiro had thrown Rin in the basement and locked the door. He told him to stay there until everything was over. The floor had caved in and a giant portal had opened up. Out of it came dozens of middle and low ranked demons as well had the Demon God himself. Out there, Shiro Fujiomoto and the priests who worked at the monastery were in a full on battle. While they fought, Rin was trapped in a dusty old basement banging on the door and screaming for someone to let him out. 

He felt hopeless, the man who had raised him was having the fight of his life. And there was nothing he could do about it but sit there on the dirty floor and wait for someone to open the door. 

Yukio was out God knows where doing God knows what. Yukio was always out busy, either with school work or doing his secret errands that he supposedly couldn't tell Rin about. He thought that they told each other everything, they were supposed to be close. He felt his heart ache. He and Yukio were close, I mean _really_ close. 

They used to spend all their time together, now Rin just sits at home and waits for Yukio to come back like a puppy waiting for their owner. It was pathetic really. He felt pathetic. Yukio was in some kind of fancy, prestigious school for Richie Riches and Smarticle Particles. He was neither of those things. He had actually dropped out of school, it had been proven too much for him. He was always getting suspended for beating other kids up when really he was just being provoked. He also had trouble learning, father Fujimoto thinks it's a learning disability. 

He gets specially taught at home by father Fujimoto or the other guys at the church when father was busy. He also couldn't seem to keep a fucking job. Yukio always looked so disappointed when Rin would come home and say he got fired. Really his employees just never liked him and got him fired. He always messed things up, he couldn't do anything. Well now, he'd do something. 

_"If something is to happen to me, guard this sword with your life!"_ Father Fujimoto told him to never unsheathe the sword. If he did, he'd never be able to live the life of a normal human again. Then he thought to himself. When had he ever been able to live a normal life? Being told he was the son of Satan at the young age of five. Constantly having demons following him around calling him their king. His life was never normal to begin with, he had nothing to lose. With that he kicked the door down and ran outside. 

"Rin! What are you doing?! Get back in that basement now! It's not safe!" 

"Shut up old man!" He yelled. He ran out in front of Satan who had possessed the body of one of the priests. He held his sheathed sword out and stood in a defensive stance. 

"Hello my son. It's me, daddy. Miss me?!" He said with a wicked laugh at the end. 

"Why are you doing this?! Leave now!" Rin yelled. 

"Hahahahaha!" Satan chuckled. "You don't scare me boy! You're an infant compared to me." 

Rin growled, yes, growled. 

"Rin!" Shiro yelled. He pushed Rin out of the way and stood defensively in front of him. "Stay away from _my_ son demon!" Satan's wicked smiled dropped when the exorcist referred to _his_ son, as his child. Shiro recited St. Michaels exorcism prayer in attempt to remove the demon from the priest before he was burned alive. That only seemed to bother Satan more. A demon pushed Rin toward the portal, he nearly fell in before regaining his balance. Satan smiled his wicked grin again and pushed father Fujimoto into Gehenna's gate. He yelled as he slowly got sucked inside. Rin only had a split second to think of what to do. 

He disobeyed his caregivers orders and drew his sword awakening his flames. The demon king smiled seeing Rin unlock his demonic powers. 

"Yes my boy! Come now! Join me." 

"HAAAAAAAAGH!" He yelled out an inhuman yell and slammed his sword into the gate with all his might, he was destroying the gateway. 

"No! What are you doing?!" He yelled. "You fool!" 

He continued to slash and destroy the gateway. Satan's vessel was running out of life, meaning he was running out of time. With one final slash the portal was destroyed, spitting father Fujimoto out and sucking Satan back in since he had been standing near it. Leaving his vessel last minute, the priest had dropped half dead. He was taken to the ER with severe burns and was sent to get purified to prevent getting possessed like that again. 

Rin placed his sword back in its casing. 

They watched the priest get carried away in the ambulance. 

Shiro had a stern look on his face. 

"You disobeyed me." 

"Eh? I saved your life old man! You should be grateful." 

"I told you to stay in the basement." He ignored Rin's last comment. "You blatantly ignored my instructions. You could've gotten seriously hurt!" 

"Now look at you." He continued. He was referring to Rin's appearance. He now had slightly pointed ears, small fangs, and a long black tail with fluff at the bottom. "You realize that your life will never be normal again, right?" 

"My life was never normal to begin with." Rin said keeping his head straight forward. 

"RIN!" He heard someone call out his name. He turned and saw Yukio running toward him. When he finally reached him he had pulled him into a tight embrace. 

"Rin!" He pulled away from him slightly. "Are you alright?! Let me look at you." A worried Yukio said to him checking his body for any injuries. 

"I'm fine Yukio." He said softly. Yukio looked at him more closely. 

"Uh, Rin?" He said confused to why he had a tail that was waving side to side behind him. 

"I'll tell you later." 

Yukio nodded. 

"So you're ok?" 

Rin smiled and nodded back at him, they were still holding each other.

"Good." Yukio planted a sweet, closed mouth kiss on the lips. Shiro Fujiomoto saw the whole thing. He accepted their relationship. Yuri had accepted their feelings for each other too while she was still alive. They weren't dating yet when she was around, but it was pretty obvious they liked each other. 

At this point Yukio was placing quick little kisses all over Rin's face whiles Rin was giggling. 

"Stop it Yuki! That tickles.~" 

Shiro shook his head and went back inside the monastery to check out all of the damage that had been done; and try to figure out specifically how much it would cost to get the building repaired. Sure enough the church was in shambles and some things had been burnt from both Satan and Rin's fighting. 

  
~*~*~*~*~*~

_~Later that night~_

_"Aah~ hah Y-Yuki! Mmmph! ...Yukio harder!"_

_"Rin~!"_

_"YUKI~!!"_

Shiro's eyes were wide open, it was 10:00 at night and he was trying to sleep. There was thin walls in the monastery. He had a pillow over his head trying to block out the sounds. Yukio had come home for the weekend, plus he wanted to stay close to Rin to make sure he was ok after everything that happened. 

_"Nngh!..Y-Yu-ki-o I'm...hah~close."_

This was going to be a long night. 

**Notes for the Chapter:**

> I apologize for the surprise smut in the end :")

**Author's Note:**

> This story was originally posted on Wattpad. To read ahead go to Wattpad. My Wattpad username is the same username as it is on AO3.


End file.
